The increasing use of traffic infrastructures entails various challenges in the fields of managing traffic and enforcing various regulations on restrictions of vehicles specific roads, as well as planning of maintenance cycles. To address such issues there is a growing need for monitoring of road traffic. The monitoring of traffic requires multiple parameters to be recorded from the roads; size and weight of vehicle, its speed, as well as the deformation each vehicle causes in the road. However, current road monitoring systems involve too many separate electronic measurement elements; induction loops, radars, cameras, and weigh-in-motion systems. This configuration results in an expensive installation with data acquisition units for each unit as well as signal and power connections to each part of the system.
EP2372322 notes that a reduction in the amount of cabling can be achieved by employing optic sensors for example, designed as Fiber Bragg Gratings disposed in a single optic fiber. The sensor device disclosed therein comprises an elongated support, which is disposed transversely in relation to the carriageway under the carriageway. The support is provided with a plurality of measuring zones, which are separated from one another in the longitudinal direction of the support by intermediate zones. The axial rigidity of the measuring zones in a direction perpendicular to the carriageway is greater than the axial rigidity of the intermediate zones in a direction perpendicular to the carriageway. Each measuring zone is provided with at least one sensor to measure deformation of this measuring zone in response to a force exerted substantially perpendicular to the carriageway. The elongated support is provided by an I-beam. When a vehicle traverses the carriageway, the I-beam subsequently deforms in a first direction, assumes a neutral state and deforms in a second direction opposite to the first direction. During deformation in the first direction, an optic sensor on the front side of the I beam subsequently is compressed by the I-beam, assumes a neutral state, and is stretched. An optic sensor on the opposite side of the I-beam subsequently is stretched, assumes a neutral state and is compressed. The optic sensors are, for example, designed as Fiber Bragg Gratings.
The support may be provided with a protective sleeve to protect the operation of the sensors against environmental influences, the support is optionally incorporated in a trough-shaped housing with a base and vertical side walls. The known sensor device is relatively costly. The protective sleeve is not strictly necessary. In the absence of this protective sleeve, the space between the flanges of the I-beam will be filled with asphalt, or other material used for construction of the carriage way. Often the space between the flanges will only be filled partially, and to an extent which can not be predicted. This is unfavorable for the reliability and accuracy of the measurement results obtained with the sensor device. Also, it is to be noted that the I-beam is an intermediate element that changes the physical characteristics to be measured, in consequence, the characteristics measured are indirect effects of the traffic on the infrastructure not reflecting the true behavior of such infrastructure.
Moreover, the use of an I-beam requires more space to be installed properly which limits the amount of sensors per linear meter that can be placed on a monitoring device.
Furthermore, the use of I-beams due to their continuous form-factor can result in cross-talk subsequent sensors thereby inducing errors into the measurement.